I wish Duncan would update the site. Only the "4" & "6" list the model number. I have the "9" box, so by process of elimination, I can figure out that the Vintage Hot Stack Plus is the "7". Also, the DCR numbers on the STK-4 series are messed up. If you look at each individual pup, they list as: N/M/B - 8.7k/8.6k/8.5k. (I didn't get that backwards. That's how they're listed.) Then, if you select "set", they all list as 8.5k, but the "details" says that the bridge is wound hotter.
So, they break down like this:
Plus Series (All the "Plus" series are A5 mags.)
-----------------------------------------------------------------
STK-4: Classic Stack Plus N/M/B = 8.7k/8.6k/8.5k (Set = 8.5k)
STK-6: Custom Stack Plus N/M/B = 14.5k
STK-7: Vintage Hot Stack Plus N/M/B = 11.9k
STK-9: Hot Stack Plus Bridge = 20.3k
-----------------------------------------------------------------
Other
-----------------------------------------------------------------
Hot Stack Strat: N/M = 13k, B = 19.9k Cer
YJM Fury Strat: N/M/B = 25.5k/25.5k/25.7k A5
-----------------------------------------------------------------
It's also odd that some list "set", while others list "neck/middle/bridge."